|
Problem IT15741
|
Status: Closed |
POSSIBLE INCORRECT COST/IO ESTIMATION IN NLJOIN WHEN ITS OUTER CARDINALITY IS ONE OR LESS |
| product: |
DB2 FOR LUW / DB2FORLUW / A50 - DB2 |
| Problem description: |
In rare occasions, DB2 optimizer can estimate incorrect cost in
NLJOIN when the outer of the NLJOIN has 1 row or less. The
incorrect estimation can be noted in query plan as the IO cost
of the NLJOIN is less than its inner IO cost.
The following is an example. The IO Cost of the NLJOIN is 4;
while the IO Cost of the inner is 215.914.
Rows
RETURN
( 1)
Cost
I/O
|
1
GRPBY
( 2)
100.058
4
|
5.01006e-10
NLJOIN
( 3)
100.058
4
/-----------+------------\
1 5.01006e-10
FETCH FETCH
( 4) ( 6)
21.1635 388.876
3 215.914
/---+----\ /----+-----\ |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* DB2 V10.5FP7 and below *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* A DB2 Restriction *
**************************************************************** |
| Local Fix: |
|
| Solution |
A DB2 Restriction |
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 15.06.2016
18.07.2016
18.07.2016 |
| Problem solved at the following versions (IBM BugInfos) |
|
| Problem solved according to the fixlist(s) of the following version(s) |
